Charge Items can be found under Manage > Charge Items.
Charge items are types that are billable/payable to a booking. When you want to make an invoice, you'll need to generate a CostItem which is of a ChargeItem type. You can think of a ChargeItem as a type you want to bill, for example Transport Fees. Then you would generate a CostItem of ChargeItem type. The CostItem will then be invoice-able. The ChargeItem also holds default details and amounts the CostItems should generate.
Tags
Charge items tags are ways the system modifies the behavior as described here. This section is currently work in progress.